In the medical art, ultrasonic handpieces employing a piezoelectric element (ultrasonic transducer) have hitherto been used for treatment of living tissues, such as cutting or removal of bones or teeth. As an example of such ultrasonic handpieces, JP-2005-95243-A1 discloses an ultrasonic handpiece for dental treatment, which is used for endodontic therapy, such as treatment of pulpal diseases and periapical periodontitis, or removal of tartar. The ultrasonic handpiece disclosed in this publication has an ultrasonic generator in a cylindrical body casing, and a tip attached to the distal end of the body casing and vibrated by the ultrasonic generator.
In general, this type of ultrasonic generator has, as shown in FIG. 7, front horn 71 located in the distal part of the body casing, rear horn 72 connected to the front horn 71 and located in the proximal part of the body casing, and transducer 73 arranged and held between the front and rear horns 71 and 72. In order to fix the ultrasonic generator in the body casing, and to block or reduce transmission of vibration of the transducer 73 to the body casing during treatment, transducer cover 74 is attached over and around the transducer 73. The transducer cover 74 used for this type of handpiece is usually an annular molded rubber product having elasticity, and fits over and around the transducer 73. The ultrasonic generator is placed in the body casing via the transducer cover 74, and a connector is connected to the proximal end of the body casing for supplying power and cooling water to the ultrasonic generator. When powered, the transducer 73 generates ultrasonic mechanical vibration, which is amplified by the front horn 71 and transmitted to the tip to vibrate the tip in the longitudinal direction of the front horn 71.
In clinical practice, tools and devices used in treatment are subjected to various sterilization processes after each treatment in order to prevent infection with various pathogenic bacteria among patients. Ultrasonic handpieces are not an exception and are usually subjected to high pressure steam sterilization such as autoclaving. To this end, the transducer cover used in ultrasonic handpieces is made of silicon rubber or the like material having excellent resistance to water, heat, and chemicals, so as to prevent steam and chemicals from permeating through the transducer cover and adhering to the electrodes of the transducer, which causes insulation deterioration of the transducer.
In order to enhance prevention of infection with various pathogenic bacteria among patients via medical tools and devices, it is recently recommended to subject the tools and devices to washing with hot water containing alkaline chemicals, in addition to the conventional high pressure steam sterilization or other sterilization.
However, when ultrasonic handpieces are washed with hot water containing alkaline chemicals, the chemicals often permeate the transducer cover even if it is made of silicon rubber, and adhere to the electrodes of the transducer to cause insulation degradation of the transducer. As a result, ultrasonic vibration is weakened and the original performance cannot be delivered.
Ultrasonic handpieces are also subjected to washing with hot water containing acidic chemicals, or immersion cleaning in alkaline or acidic chemicals. These procedures also have similar problems as described above.